Accepted Scientific Name: Arrojadoa rhodantha Britton & Rose
Cactaceae (Britton & Rose) 2: 170. 1920 [9 Sep 1920] Britton & Rose
Arrojadoa horstiana (Arrojadoa rhodantha) Photo by: Julio C. García
Origin and Habitat: This cactus is endemic to Brazil, where it occurs in Bahia, Piauí, Pernambuco, Minas Gerais and Goias.
Type locality: Riacho de Santana, Bahia, Brazil
Altitude range: 220 to 1,200 metres above sea level.
Habitat and Ecology: Arrojadoa rhodanthaSN|4866]]SN|4847]] can be found in very arid areas in the underwood of the Caatinga on various substrates (including the shade of dense caatinga forest and in the open on inselbergs), and entering the caatinga/campo rupestre ecotone. In the same area the following cactus species can also be found: Arrojadoa penicillataSN|4847]]SN|4866]], Cereus jamacaruSN|8073]]SN|6995]], ColeocepbaloCereus goebelianusSN|6995]], Melocactus salvadorensisSN|26074]]SN|26074]] and Tacinga inamoenaSN|19087]]SN|19087]]. This species is widespread and common throughout its range. The subpopulations have suffered from declines due to habitat loss. The habitat is under degradation due to deforestation for logging and for agriculture, cattle ranching, urbanization, quarrying, as well as due to fires.
Synonyms:
See all synonyms of Arrojadoa rhodantha
Description: Arrojadoa rhodanthaSN|4847]]SN|4847]] is a shrubby cactus, at first erect, afterwards branching basally and clambering. It can reach a height of over one metre. Every year the tubulaar violet-red flowers are produced in clusters from a cephalium at the top of the joints. A. rhodantha is fairly variable and several controversial subspecies and varieties have been described.
Stems: Joined 1 to 2 meters long. Joints short cylindric, flattened at the top, dark green 20-40(-50) mm thick.
Roots: Fibrous.
Ribs: Ten to twelve, fairly shallow.
Areoles: Small, with short wool, in close proximity, usually less than 1 cm apart.
Spines: At first brown, in age white when young accompanied by some long cobwebby hairs.
Central spines: 5-6, similar to the radials except a little longer and stouter to 3 cm long.
Radial spines: About 20, to 12 mm long.
Pseudocephalia (flower bearing structures): At the tops of the joints with 1 .5-2 cm long brown wool and up to 3 cm long reddish brown bristles.
Flowers: Deep pink to violet-red, diurnal at the upper areoles, forming in clusters of 12 to 14 in a pseudocephalium at the tops of branches, 3 to 4 cm long, 1.2-2(-3) cm in diameter, nearly cylindric, the tube short pink, rigid, ovary and lower part of tube naked. Perianth-segments in several rows, short, erect, uppermost scales and perianth-segments similar, obtuse. Stamens numerous, included.
Fruits (berries): Red, naked, juicy oblong to obovate, about 2 cm long.
Seeds: Small, black.
Chromosome number: 2n = 22
Subspecies, varieties, forms and cultivars of plants belonging to the Arrojadoa rhodantha group
Bibliography: Major references and further lectures
1) Machado, M., Braun, P., Taylor, N.P. & Zappi, D. 2013. Arrojadoa rhodantha. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 16 August 2014.
2) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
3) James Cullen, Sabina G. Knees, H. Suzanne Cubey "The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass" Cambridge University Press, 11/Aug/2011
4) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
5) N. L. Britton, J. N. Rose: “The Cactaceae. Descriptions and Illustrations of Plants of the Cactus Family.” Volume 2, The Carnegie Institution of Washington, Washington 1920
6) Haustein, Erik “Der Kosmos-Kakteenführer” Franckh-Kosmos 1983
7) Cullmann W., Götz E., Gröner G.”Kakteen: Kultur, Vermehrung und Pflege - Lexikon der Gattungen und Arten” Ulmer, Stuttgart, 1984
8) Willy Cullmann, Erich Götz (Dozent Dr.), Gerhard Gröner “The encyclopedia of cacti” Timber Press, 1987
9) Clive Innes “Complete Handbook of Cacti and Succulents” Van Nostrand Reinhold Company, 01/Dec/1981
10) Urs Eggli, Leonard E. Newton: “Etymological Dictionary of Succulent Plant Names”. Springer, Berlin/Heidelberg 2010
11) Juliana P. Castro, Luiz G.R. Souza, Lânia F. Alves, Ana E.B. Silva, Marcelo Guerra & Leonardo P. Felix. 1073 Marhold (ed.) “IAPT/IOPB chromosome data 15” TAXON 62 (5) • October 2013: 1073–1083
Cultivation and Propagation: These tropical cacti are not the easiest things to grow and aren’t plants for beginners. With their snake-like growth they are ideal cactus for hanging baskets.
Growth rate: It is a relatively rapidly growing given the best conditions.
Soils: It requires a rich but very porous mineral cactus mix soil.
Repotting: The root system is weak and generally resents being repotted and can take a long time to re-establish. Use pot with good drainage.
Light: They prefer very bright light, not as much as the most arid growing cacti, but plenty nonetheless. Tends to bronze in strong light, which encourages flowering and heavy spine production.
Watering: They grow from April to October and cannot endure long stretches of total dryness, and also too much water will rot them, as their weak root systems tends to be inefficient at sucking up water from wet soil. Nonetheless, again as a result of their tropical origins, they need a fair amount of water, but allow the soil to dry quite a bit before watering again.
Fertilization: Do not feed in winter.
Hardiness: They rest from October to April but can’t stand cold, or even fairly cool temperatures, so is indispensable to keep them above 8-12°C at all times, severe damage or death occurring at temperatures that the great majority of cacti wouldn’t mind in the least and prefer more frequent water in winter than other cacti, say once a month. (but hardy to 4 C ° C for short periods). However warmth throughout the year will increase the grower's success (minimum 12° to 20° C during rest season).
Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for:
- Red spiders: Red spiders may be effectively rubbed up by misting the vulnerable plants every day
- Mealy bugs: Mealy bugs occasionally they develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Scales: Scales are rarely a problem.
- Rot: it is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much.
Propagation: Exclusively by Seeds. Sow in February-march in a light, sandy, porous soil. Cover germinating tray with glass to prevent seed from drying out. Germination is most successful at a temperature of 18 to 22° C. It can also be propagated by lateral offshoots (if available), grafting is not necessary.
Arrojadoa rhodantha Britton & Rose: has cylindrical stems over one metre long. Spines mostly brown. The tubular violet-red flowers are produced in clusters from a cephalium at the top of the joints. Distribution: Brazil, (Bahia, Piauí, Pernambuco, Minas Gerais and Goias).
